JP6435977B2 - How to change the slab width during continuous casting - Google Patents

Description

  The present invention relates to a method for changing a slab width during continuous casting, and more particularly, to a method for enlarging the slab width by moving a mold short side during continuous casting.

  Continuous casting is performed using a mold having two opposing mold long sides and two mold short sides sandwiched between the mold long sides, and the slab width is changed by changing the distance between the mold short sides. The technology to change the is widely known. Especially, the technique which changes slab width | variety, continuing continuous casting becomes very important from a viewpoint of an operation rate and a yield improvement.

In continuous casting of a slab, solidification shrinkage occurs during casting. Therefore, the mold short side and the solidified shell are appropriately in contact with each other by inclining the mold short side.
In the following description, the inclination provided on the short side of the mold is referred to as “taper”. Further, the mold upper end width−the mold lower end width = taper amount, and a state where the taper amount is large is called “taper is strong”, and a state where the taper amount is small is called “taper is weak”. The mold lower end width is a distance between the lower ends of the opposing mold short sides, and the mold upper end width is a distance between the upper ends of the opposing mold short sides.
The taper angle is an inclination angle of the mold short side with respect to a vertical line passing through the lower end of the mold short side, and is positive when the upper end of the mold short side is directed outward.

If the taper is not appropriate and the taper is strong, the short side of the mold pushes the slab and becomes a cause of slab defects. Conversely, if the taper is weak, a gap is generated between the short side of the mold and the solidified shell, which causes breakout due to insufficient cooling.
When changing the slab width, it is necessary to appropriately change the taper in order to suppress slab defects and breakout. However, an appropriate taper when moving the mold short side during continuous casting is different from an appropriate taper when casting with a constant slab width. In addition, since the amount of solidification shrinkage depends on the solidification shrinkage rate and the slab width, the appropriate taper changes from moment to moment when the mold short side moves, where the slab width continues to change. Therefore, a technique for maintaining an appropriate taper during slab width change is required.

Therefore, for example, Patent Document 1 discloses that the speed difference between the upper end of the mold short side and the lower end of the mold short side is accelerated at the start of the slab width change, and the upper end of the mold short side A method is disclosed in which the speed relationship at the lower end of the mold short side is reversed to decelerate the speed difference while keeping the speed difference constant, and the movement of the mold short side is stopped at the target slab width.
In Patent Document 2, the slab width changing operation during continuous casting is divided into three steps, and after changing the taper angle of the mold short side to an appropriate taper angle during movement of the mold short side, the mold short side is fixed. A method of moving at a speed and finally changing to an appropriate taper angle at the target slab width is disclosed. In this method, the taper is changed at the same time as changing the slab width by making the moving speed of the upper end of the mold larger than the moving speed of the lower end of the mold when the short side of the mold is moved at a constant speed.

JP-A-61-144255 Japanese Patent Laid-Open No. 3-133549

However, in the case of the method described in Patent Document 1, it is necessary to control a slight speed difference between the upper end of the mold short side and the lower end of the mold short side.
On the other hand, according to the method described in Patent Document 2, by appropriately setting the moving speed difference between the upper end of the mold short side and the lower end of the mold short side, an appropriate taper corresponding to the slab width is maintained even when the slab width is changed. However, it is necessary to control the moving speed of the upper end of the mold short side and the lower end of the mold short side very precisely. However, it is difficult to realize this industrially, and an error always occurs.

When the taper rate is defined as (mold upper end width−mold lower end width) / mold lower end width / mold height × 100 [% / m], when the mold height is, for example, 1000 mm, it is appropriate in a state where the slab width is not changed. The taper rate is a predetermined value within a range of 1 to 1.5% / m, and it is necessary to use the taper rate in units of 0.1% / m depending on the steel type composition. When 0.1% / m is converted into a taper angle, when the mold lower end width is 1 m, it becomes about 0.03 °.
When the taper is strengthened by increasing the speed difference between the upper and lower ends of the mold short side (increasing the taper angle) while moving the mold short side (increasing the slab width), the speed difference between the upper and lower ends of the mold short side is set to 1-1. It should be about 5%, and it is necessary to use properly in units of 0.1% according to the steel type component. If the moving speed of the lower end of the mold short side is, for example, 10 mm / min, the moving speed of the upper end of the mold short side is 10.15 mm / min (taper rate 1.5% / m), and the speed difference between the upper and lower ends of the mold short side is 0. .15 mm / min. Furthermore, in the above example, when the taper rate is changed (increased) in units of 0.1% / m for reasons such as different steel grade components, the speed difference between the upper and lower ends of the mold short side is in units of 0.01 mm / min. Need to be changed.
Thus, in the case of the conventional methods described in Patent Document 1 and Patent Document 2, a slight speed difference must be controlled, and the occurrence of errors is inevitable.

  Therefore, when changing the casting width by moving the mold short side during continuous casting, if the amount of change in the slab width is large, errors will accumulate and the taper angle will deviate more than the target value. The contact with the solidified shell cannot be maintained properly. As a result, slab defects caused by pressing the slab on the short side of the mold, or insufficient cooling due to the generation of voids, and breakout due to this, occur.

  The present invention has been made in view of such circumstances, and even when the amount of change in the slab width during continuous casting is large, the occurrence of breakout and slab defects can be suppressed during continuous casting. It aims at providing the slab width changing method.

  As described above, it is difficult to realize an appropriate taper angle by speed difference control, which causes slab defects and breakout. Accordingly, the inventors of the present invention have conceived the present invention by paying attention to controlling the positions of the upper and lower ends of the mold short side as control with higher accuracy than the taper angle control by speed difference control.

In the present invention, a pair of mold short sides whose slab width is set to w _S and taper angle θ _S are moved symmetrically with respect to the center axis of the mold during continuous casting, so that the slab width becomes w _L (w _L ≧ w _S +50 mm), a method of changing the taper angle to θ _L (θ _S <θ _L ), characterized by performing the following operations.
(A) The lower end width of the mold at the start of movement is w ₁ = w _S , and the lower end width of the mold at the completion of movement is w _n = w _L (n is an integer of 2 or more).
(B) In the state where the mold lower end width is w _i (i = 1,..., N−1), the upper end of the mold short side is expanded outwardly, and the taper angle of the mold short side is set to θ _i (θ _S After increasing to <θ _i ), an operation of translating the mold short side to make the mold lower end width w _{i + 1} (w _i <w _{i + 1} ≦ w _n ) from i = 1 to i = n−1 Implement sequentially.
(C) the mold bottom width decreases in the taper angle of the mold short side when it reaches the _{w n θ L (θ L <} θ n-1).

The reason why w _L ≧ w _S +50 mm in the present invention is that the problem of the present invention becomes apparent when the change width of the slab is 50 mm or more.
θ _S and θ _L are both taper angles in a state where the mold short side does not move, and are usually set to equal taper rates. However, theta for the slab width rather than theta _L wide _S, the taper angle becomes θ _{S <θ L.} The taper ratio is (mold upper end width−mold lower end width) / mold lower end width / mold height × 100 [% / m].

  The main feature of the present invention is that the upper end of the mold short side is expanded outwardly with respect to the lower end of the mold short side to increase the taper angle of the mold short side, and the mold short side is translated at the increased taper angle. This operation is repeated until the lower end width of the mold short side reaches the target slab width.

  When the slab width is increased during continuous casting, a breakout due to slow cooling may occur unless the taper angle is increased. In the present invention, the taper angle of the mold short side is increased before the parallel movement of the mold short side. The target taper angle can be easily set by changing the position of the upper end of the mold short side with respect to the lower end of the mold short side. The taper angle error in the present invention is about half of the taper angle error in the speed difference control.

Moreover, by moving the mold short side in parallel, the movement amount of the upper end and the lower end of the mold short side becomes the same, and the movement accuracy of the mold short side is ensured. The error of the movement amount is about ± 0.01 mm with respect to the target movement amount (for example, 10 mm). For this reason, unlike the speed difference control, errors do not accumulate and the taper angle is not greatly deviated from the target value.
In addition, when the parallel movement distance per time exceeds 50 mm, there is a possibility of causing breakout and slab defects, so the parallel movement distance per time is preferably 50 mm or less.

An appropriate taper when casting at a constant slab width is smaller than an appropriate taper when moving the short side of the mold during continuous casting to increase the slab width. Accordingly, when the mold bottom width reaches the slab width w _L of the target, reducing the taper angle theta _L.

  In the slab width changing method during continuous casting according to the present invention, the positions of the upper and lower ends of the mold short side are controlled, so that even when the change amount of the slab width is large, an error is hardly generated in the taper setting. Thereby, the taper of a mold short side can be maintained appropriately, and the occurrence of breakout and slab defects during the slab width change can be reduced. As a result, it is possible to prevent equipment damage, prevent productivity decline for equipment restoration, and prevent yield drop due to occurrence of slab defects.

It is a schematic diagram of the casting_mold | template used for the slab width changing method during the continuous casting which concerns on one embodiment of this invention. FIG. 5 is a schematic diagram of a mold width direction cross section when the upper end of the mold short side is expanded outwardly with respect to the stopped mold short side lower end to increase the taper angle of the mold short side. (A) The graph which showed the relationship between the mold lower end width and the taper rate in the implementation process of the slab width changing method during continuous casting according to one embodiment of the present invention, (B) The mold short in the implementation process of the method It is the schematic diagram which showed the movement condition of the edge | side. It is the graph which showed the relationship between the casting mold lower end width | variety and taper angle in the implementation process of the slab width changing method in the continuous casting which concerns on the embodiment.

  Next, embodiments of the present invention will be described with reference to the accompanying drawings to provide an understanding of the present invention.

  The schematic diagram of the casting_mold | template 10 used for the slab width changing method in the continuous casting which concerns on one embodiment of this invention is shown in FIG. As shown in the figure, a mold 10 for casting a slab S includes a pair of mold long sides 12 arranged opposite to each other, and a pair of mold short sides 11 sandwiched and opposed by a pair of mold long sides 12. Yes. Actuators 13 for moving the mold short side 11 in the mold long side direction are attached to the upper and lower ends of the back surface of each mold short side 11. The mold short side 11 is moved and tapered by controlling the actuators 13 arranged in two upper and lower stages.

A pair of mold short sides 11 having a slab width set to w _S and a taper angle set to θ _S are moved symmetrically with respect to the central axis of the mold 10 during continuous casting to set the slab width to w _L (w _L ≧ w _S +50 mm), and the procedure for changing the taper angle to θ _L (θ _S <θ _L ) is shown below.
However, θ _S is a taper angle corresponding to an appropriate taper rate when the slab width is constant at w _S , and θ _L is a taper angle corresponding to an appropriate taper rate when the slab width is constant at w _L. is there.

[STEP-1] The mold lower end width at the start of movement is w ₁ = w _S , and the mold lower end width at the completion of movement is w _n = w _L (n is an integer of 2 or more). Set. However, the parallel movement distance Δw per time may be a variable value instead of a constant value. Moreover, it is preferable that the parallel movement distance (DELTA) w per time is 50 mm or less.

[STEP-2] The following operations are sequentially performed from i = 1 to i = n-1.
(1) In the state where the mold lower end width is w _i , the upper end of the mold short side 11 is extended outward with respect to the lower end of the stopped mold short side 11 so that the taper angle of the mold short side 11 becomes θ _i . Increase. The taper angle θ _i is a taper angle corresponding to an appropriate taper ratio when the upper end of the mold short side 11 is expanded outward with respect to the lower end of the mold short side 11 stopped.
(2) The mold short side 11 is translated while maintaining the taper angle at θ _i , and the mold lower end width is set to w _{i + 1} (w _{i + 1} = w _i + Δw).

[STEP-3] the mold bottom width decreases the taper angle of the mold short side 11 when it reaches the _{w n} to _{θ L (θ L <θ n} -1).

  Here, an appropriate taper ratio when the taper angle of the mold short side 11 is increased by expanding the upper end of the mold short side 11 outward with respect to the lower end of the mold short side 11 stopped will be described. The appropriate taper rate when the mold short side 11 moves is a taper rate considering the casting speed and the moving speed of the mold short side 11.

FIG. 2 shows a cross section in the mold width direction when increasing the taper angle of the mold short side 11 by expanding the upper end of the mold short side 11 outward with respect to the lower end of the mold short side 11 stopped.
When the taper amount of the mold short side 11 before the movement is T, is _{T =} W U -W _D. Incidentally, _{W U} a template upper width, is _{W D} is the mold lower end width.
When the time for the molten steel to descend to the lower end of the mold is Δt, Δt = h / Vc. However, h is a molten steel depth and Vc is a casting speed.
On the other hand, the amount of movement of the mold short side 11 at the molten metal surface position accompanying the movement of the mold short side 11 is VmΔt. Vm is the moving speed of the mold short side 11.

Therefore, the movement amount ΔT that the upper end of the mold short side 11 moves during Δt is expressed by the following equation. Here, L is the mold height.
ΔT = VmΔt × L / h = Vm × L / Vc
Therefore, an appropriate taper ratio α when the mold short side 11 is moved is expressed by the following equation.
α = (T + 2ΔT) / W _D / L
Further, the taper angle θ corresponding to the taper rate α is calculated by the following equation.
θ = arcsin ((T + 2ΔT) / 2 / L)

Next, the procedure for changing the slab width of low-carbon steel continuously cast at a casting speed of 1.5 m / min from 980 mm to 1200 mm using the slab width changing method during continuous casting according to this embodiment. Is described below. In addition, the moving speed of the mold short side is 10 mm / min, and the mold height is 900 mm.
FIG. 3A shows the relationship between the mold lower end width and the taper ratio in the process of changing the slab width during the continuous casting according to the present embodiment, and FIG. 3A shows the movement of the mold short side in the process of executing the method. 3 (B). Moreover, the relationship between the mold lower end width and the taper angle is shown in FIG.

(1) The mold lower end width before starting the slab width change is 980.0 mm, the mold upper end width is 992.7 mm, the taper rate is 1.44% / m, and the taper angle is 0.40 °.
(2) The taper angle of the mold short side is increased to 0.79 ° by spreading the upper end of the mold short side outward with respect to the lower end of the stopped mold short side. At this time, the upper end width of the mold is 1004.7 mm, and the taper ratio is 2.80% / m.
(3) When the mold short side is translated in a state where the taper angle of the mold short side is maintained at 0.79 °, the mold short side is reached when the mold lower end width becomes 1030.0 mm and the mold upper end width becomes 1054.7 mm. Stop parallel translation. The taper rate at that time is 2.66% / m.

(4) The taper angle of the mold short side is increased to 0.81 ° by spreading the upper end of the mold short side outward with respect to the lower end of the stopped mold short side. At this time, the upper end width of the mold is 1055.3 mm, and the taper ratio is 2.73% / m.
(5) The mold short side is translated when the taper angle of the mold short side is maintained at 0.81 °, and when the mold lower end width becomes 1080.0 mm and the mold upper end width becomes 1105.3 mm. Stop parallel translation. The taper rate at that time is 2.61% / m.

(6) The taper angle of the mold short side is increased to 0.83 ° by spreading the upper end of the mold short side outward with respect to the lower end of the stopped mold short side. The mold upper end width at this time is 1106.0 mm, and the taper rate is 2.67% / m.
(7) The mold short side is translated when the taper angle of the mold short side is maintained at 0.83 °, and when the mold lower end width becomes 1130.0 mm and the mold upper end width becomes 1156.0 mm. Stop parallel translation. The taper rate at that time is 2.56% / m.

(8) The taper angle of the mold short side is increased to 0.85 ° by spreading the upper end of the mold short side outward with respect to the lower end of the stopped mold short side. The mold upper end width at this time is 1156.6 mm, and the taper rate is 2.62% / m.
(9) The mold short side is translated when the taper angle of the mold short side is maintained at 0.85 °, and when the mold lower end width becomes 1180.0 mm and the mold upper end width becomes 1206.6 mm. Stop parallel translation. The taper rate at that time is 2.51% / m.

(10) The taper angle of the mold short side is increased to 0.87 ° by spreading the upper end of the mold short side outward with respect to the lower end of the stopped mold short side. At this time, the mold upper end width is 1207.3 mm, and the taper rate is 2.57% / m.
(11) When the mold short side is translated in a state where the taper angle of the mold short side is maintained at 0.87 °, the mold lower end width becomes 1200.0 mm (target width), and the mold upper end width becomes 1227.3 mm. Stop the parallel movement of the short side of the mold. The taper rate at that time is 2.53% / m.

(12) The upper end of the mold short side is narrowed inward with respect to the lower end of the stopped mold short side to reduce the mold upper end width to 1215.6 mm. The taper rate upon completion of movement is 1.44% / m, and the taper angle is 0.50 °.

In the above operation, the difference between the actual taper and the appropriate taper is the largest when the lower end width of the mold is 1030 mm and the upper end width of the mold is 1054.7 mm. 0.07% / m).
Further, when the control is performed by monitoring the displacement amount of the mold short side, the speed error is not accumulated, and only the error due to the stop accuracy occurs. This error is about ± 0.2 mm.
On the other hand, when the lower end speed of the mold short side is controlled at 10 mm / min and the upper end speed of the mold short side is controlled at 10.13 mm / min (speed difference: 0.13 mm / min), the accuracy of speed control is ± 0.05 mm / min. If min, an error of ± 1.1 mm (taper rate of 0.10% / m when the mold lower end width is 1200 mm) may occur. In speed control, in addition to this error, an error of ± 0.2 mm due to the stopping accuracy can also occur.

  Although one embodiment of the present invention has been described above, the present invention is not limited to the configuration described in the above-described embodiment, and is within the scope of matters described in the claims. Other possible embodiments and modifications are also included.

10: mold, 11: mold short side, 12: mold long side, 13: actuator, S: slab

Claims (1)

A pair of mold short sides with a slab width set to w _S and a taper angle set to θ _S are moved symmetrically with respect to the center axis of the mold during continuous casting to set the slab width to w _L (w _L ≧ w _S +50 mm). The taper angle is changed to θ _L (θ _S <θ _L ),
The mold lower end width at the start of movement is w ₁ = w _S , and the mold lower end width at the end of movement is w _n = w _L (n is an integer of 2 or more),
In the state where the lower end width of the mold is w _i (i = 1,..., N−1), the upper end of the mold short side is expanded outwardly, and the taper angle of the mold short side is set to θ _i (θ _S <θ _i ), The operation is performed sequentially from i = 1 to i = n−1 by translating the short side of the mold to make the mold lower end width w _{i + 1} (w _i <w _{i + 1} ≦ w _n ). ,
Slab width changing method in a continuous casting the mold bottom width, characterized in that reducing the taper angle of the mold short side when it reaches the w _n to _{θ L (θ L <θ n} -1).

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